New car deck worked for 10 seconds, now it and old deck won't work?

You're deck has both live and on/off feed. constant current for memory. It's probably just a fuse, should have disconnected bat. before installing. Make sure no bare wires behind deck,tape each as needed. There are fuses under hood and under left side of dash. look for blown fuse in both. Hopefully will work after replacing. Lesson learned always unhook power source when doing electrical repairs or mods.